Douglas-fir tussock moth

Douglas-fir tussock moth caterpillars defoliate Douglas-fir, fir, and spruce trees in Western Washington starting from tree tops and working downward, consuming new growth. You will see browning foliage at the crown first, then increasing defoliation down the canopy. Tussock moth caterpillars have distinctive tufts of hair and can cause severe needle loss in a single season. Trees severely defoliated over multiple years may die. Caterpillar hairs may cause skin irritation on contact.

Single-year defoliation is often survivable, but repeated attacks weaken trees and invite bark beetles. Prune infested branch tips if populations are light. Apply Bacillus thuringiensis (Bt) to new foliage if timed before heavy feeding. Accept natural enemy suppression of outbreaks within three years.